Some diseases such as tumors, chronic urticaria and lung diseases are able to be diagnosed by blood test. Before taking the blood test, a blood sample contained in a test tube is left and untouched for a particular period of time until the blood sample is in a stable state. Then, a medical worker will bring the test tube to a blood testing device, and use a syringe and a tube to draw the blood sample. The drawn blood sample is then transferred into a test chip. Then, a light source generates light incident on the test chip, and then a camera captures a cell image of the blood sample in the test chip for helping the medical worker to diagnose the diseases.